Remediation of bromate contaminated groundwater

Abstract

Bromate (BrO3") is a by-product formed at concentrations of 0.4
-
60 µg L'' during
potable water ozonation. Following World Health Organisation designation as a `possible
human' carcinogen, a 10 pg L" drinking water limit was introduced in England and Wales.
Discovery of bromate contamination within a UK aquifer highlighted a knowledge gap,
addressed by this project, relating to environmental behaviour and groundwater
remediation.
Following selection of an anion analysis strategy utilising Ion Chromatography (IC),
bromate behaviour in wastewater was investigated as contaminated groundwater ingress to
treatment processes was deemed possible. Respiration of wastewater biomass was
unaffected by spiking of < 200 mg Ul bromate or bromide, with pilot-scale process dosing
trials (S 100 mg L') using a Membrane Bioreactor (MBR) also exhibiting little negative
effect following biomass acclimation.
Bromate reduction to bromide was observed in a continuous-flow suspended growth
chemostat bioreactor at retention times of 20
-
80 hours. A biological mechanism was
confirmed in this system, with reduction mediated by indigenous groundwater bacteria
following glucose addition. Bromate reduction rates were initially low (5 27.8 pg U' hr 1),
but acclimation increased rates to > 1000 pg L" hr t. An alteration in microbial
composition was noted over this period, from a denitrifying `co-metabolic' culture to
predomination of `high-rate' specific bromate degraders. Operational parameters including
pH, temperature, carbon source, influent bromate and glucose, and retention times were
investigated, with all parameters apart from pH shown to affect bromate reduction rates.
For example increased bromate influent enhanced reduction rate, although potentially toxic
effects were noted with an influent > 75
-
80 mg L"'. Batch studies suggested glucose was
rapidly fermented (< 48 hours) by the microbial consortium. Nitrate was also rapidly
removed (< 4 hours), with sulphate reduction only following removal of bromate. A fixed-
film pilot-scale bioreactor system, seeded with biomass from the chemostat culture,
reduced > 90% of a 1.1 mg L"1 bromate influent within unspiked contaminated
groundwater. Plating studies were successful in producing a range of isolates from the
mixed chemostat culture. Overall the project demonstrated, for the first time, continuous
remediation of bromate groundwater contamination within a bioreactor system